1. Field of the Invention
The present invention relates to a technology for processing biometric information input for authentication, and particularly to a method for partially and successively collecting biometric information.
2. Description of the Related Art
In a common biometric authentication device, biometric data (enrollment data) is previously prepared (recorded) from biometric information and further biometric data (matching data) is created from biometric information to be authenticated, and then, the matching data is compared to the enrollment data for authentication.
For biometric authentication, biometric information that is common to all persons and consistent throughout the lifetime of a person (e.g., fingerprint, palm print, finger vein, palm vein, etc.) is used, but there are problematic situations in which authentication fails due to various factors.
Further, such authentication failures can be grouped into two major factors. The first factor is that although both enrollment data and matching data are related to the same person, the person is falsely identified as a different person and such case is called “false rejection”. The second factor is that although enrollment data and matching data are related to a different person than a person himself/herself, the different person is falsely identified as the person himself/herself and such case is called “false acceptance”.
Further, conventionally, a variety of methods for matching biometric information have been put into practice, however, in some of those methods, authentication sometimes fails due to rotational displacement of biometric information. That is, when the degree of freedom which is of the rotation of a living body relative to a biometric information input device, or vice versa, is large, rotational displacement exceeds an acceptable range for a matching method and false rejection rate increases. Moreover, although a method for repeating matching while rotating matching data or enrollment data, in order to accommodate the degree of freedom in the rotational direction, has been also known, rotating the matching data or enrollment data sometimes causes matching data and enrollment data corresponding to different persons to accidentally match, leading to an increase in false acceptance rate.
A sweep fingerprint sensor has been known as a biometric information input device. The sweep fingerprint sensor has a rectangular collection surface (sensor surface/capturing surface) of a small size and with a length substantially shorter than that of a finger. Further, while a finger is moved relative to the collection surface or the collection surface (fingerprint sensor) is moved relative to the finger, a plurality of partial images of a fingerprint of the finger are successively collected by a fingerprint sensor and a total fingerprint image is reconstructed by the collected partial images. Minutia information (ridge bifurcation and ending) is extracted and created from the reconstructed fingerprint image and the above personal authentication is performed based on the information. Note that relative movement of finger to the collection surface as described above is called “sweeping” or “sliding”.
A fingerprint reading device provided with such a sweep fingerprint sensor is disclosed, for example, in the following Patent Documents 1, 2. Further, a method for reconstructing a fingerprint image using the amount of parallel movement and the amount of rotational movement detected by the sweep fingerprint sensor is disclosed in the following Patent Document 3.
As disclosed in the following Patent Documents 1 to 3, the sweep fingerprint sensor operates so that relative position of a sensor and a finger is changed and then the partial images of the finger are input to the sensor in order. Note that hereinafter, operation of changing the relative position of a sensor and a finger is called “sliding” and a direction (movement direction of finger) in which the relative position is changed is called “slide direction”. Typically, the sweep fingerprint sensor causes a finger to slide relative to the sensor toward the front side (the side of a subject to be authenticated), during which the sensor successively acquires partial images of the finger.
For example, the above Patent Document 3 discloses a method for detecting the slide direction and when the detected slide direction is opposite to a previously expected direction, interrupting input of fingerprint images. That is, a conventional fingerprint image input device imposes a restriction on the slide direction.    [Patent Document 1]    Japanese Patent Laid-Open No. Hei 10-91769    [Patent Document 2]    Japanese Patent Laid-Open No. Hei 11-253428    [Patent Document 3]    Japanese Patent Laid-Open No. 2004-110438
Recently, some of portable information processing devices provided with a sweep fingerprint sensor and typified by laptop PC (Personal Computer), PDAs (Personal Digital Assistants), portable phone and the like are tailored to be used, oriented in the up/down direction or left/right direction.
However, in such a conventional information processing device, when a fingerprint image is input using a sweep fingerprint sensor, the device has to cause a finger to slide in the previously expected direction and therefore needs to rotate itself to read a fingerprint, thereby disadvantageously increasing the degree of complexity. Further, in a fingerprint image input device provided with as a sweep fingerprint sensor that utilizes a change in relative position of a sensor and a finger, it is desirable to cause the sensor to be much more insensitive to the rotational displacement of a fingerprint image due to the slide movement of the finger.
Moreover, detection of the slide direction in the sweep fingerprint sensor is achieved by comparing a plurality of successive partial images acquired by the sensor and calculating a relative position corresponding to the largest degree of overlap. However, the sensor needs to acquire the partial images in a shorter time interval so that the images are overlapped one another even when a finger slides quickly, which imposes a heavy load on the sensor to detect the slide direction. That is, a series of processing steps requiring a large amount of calculations are performed as follows. For example, the relative position of a sensor and a finger is shifted little by little and the degree of overlap in an overlap area of the images is determined, and then, the slide direction is detected based on the relative position corresponding to the largest degree of overlap. Therefore, there is also a problematic situation in which the sensor needs to efficiently detect the slide direction.
Additionally, an authentication technology using biometric information utilizes, as biometric information, a site typified by a body site such as a fingerprint having characteristics common to all persons and consistent throughout the lifetime of a person. However, even such biometric information could not cause a person to be identified as the person himself/herself in the event where different sites are input when enrolled and matched. This requires the biometric information input device to increase reproducibility of a position on which biometric information will be input.
In order to increase the reproducibility of a position on which biometric information will be input, it is useful to allow a user to view, for confirmation, the input biometric information image. However, in a device tailored to be used, oriented in an up/down or left/right direction, biometric information image to be input is displaced in the rotational direction, potentially preventing the user from viewing, for confirmation, the image information. Accordingly, this also requires the device to display biometric information image so that rotation of the device never affects the display of the biometric information image.
Further, for example, if biometric information image is read and a finger placed on the sensor is displaced significantly from the center of the sensor, it is proposed that the device indicates an instruction as a message, for example, “move your finger closer to the right” to a user and instructs the user's finger to move to an appropriate position on the sensor. However, for example, in a device provided with a fingerprint sensor that can be used, oriented in the up/down direction, a direction viewed from the device and a direction viewed from the user are opposite in such an upside down position of the sensor and therefore the device has to take into account the status, etc., (orientation, pointing direction) of the device in order to instruct the user to move his/her finger in the proper direction, which imposes an additional task on the device.
Further, it could also be proposed that a sweep fingerprint sensor is used as a pointing device. However, in a device that can be used, oriented in an up/down or left/right direction, when a sweep fingerprint sensor is used as a pointing device, a direction viewed from the device and a direction viewed from a user are different and therefore direction information detected using a pointing function is sometimes displaced from a direction the user inputs.